Infrared Spectroscopy

Transcription

1 This book is an introductory text designed to acquaint undergraduate and graduate students with the basic theory and interpretative techniques of infrared spectroscopy. Much of the material in this text has been used over a period of several years for teaching courses in materials characterization and chemical analysis. It presents the infrared spectra of the major classes of organic compounds and correlates the infrared bands (bond vibrations) of each spectrum with the structural features of the compound it represents. This has been done for hydrocarbons, organic acids, ketones, aldehydes, esters, anhydrides, phenols, amines, and amides. The text discusses the origin of the fragments, techniques, innovations, and applications in infrared spectroscopy. It is interspersed with many illustrations, examples, an adequate but not overwhelming bibliography, and problems for students. It will serve as a lecture text for a one-semester course in infrared spectroscopy or can be used to teach the infrared spectroscopy portion of a broader course in material characterization and chemical analysis. V647 ISBN Thompson James M. Thompson is emeritus professor at the Department of Chemistry and former chair of the Department of Natural and Physical Sciences at Alabama A&M University. He taught organic chemistry and instrumental methods for many years at the university. He received his PhD in 1975 from the University of Delaware under the supervision of Dr. Richard F. Heck (recipient of the Nobel Prize in Chemistry in 2010). Prof. Thompson s research interests are in organic chemistry, use of mass spectra, infrared spectra, C-13 and proton nuclear magnetic resonance spectra, and structural determination of organic compounds. He performed research for NASA in the area of thermal gravimetric analysis for about 15 years and is a recipient of more than 50 awards and recognitions. Infrared Spectroscopy It is estimated that there are about 10 million organic chemicals known, and about 100,000 new organic compounds are produced each year. Some of these new chemicals are made in the laboratory and some are isolated from natural products. The structural determination of these compounds is the job of the chemist. There are several instrumental techniques used to determine the structures of organic compounds. These include NMR, UV/visible, infrared spectroscopy, mass spectrometry, and X-ray crystallography. Of all the instrumental techniques listed, infrared spectroscopy and mass spectrometry are the two most popular techniques, mainly because they tend to be less expensive and give us the most structural information. Infrared Spectroscopy James M. Thompson

2 Infrared Spectroscopy

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4 Infrared Spectroscopy James M. Thompson

5 Published by Pan Stanford Publishing Pte. Ltd. Penthouse Level, Suntec Tower 3 8 Temasek Boulevard Singapore editorial@panstanford.com Web: British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. Infrared Spectroscopy Copyright c 2018 Pan Stanford Publishing Pte. Ltd. All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the publisher. For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher. ISBN (Hardback) ISBN (ebook)

6 To my daughter, Christine

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8 Contents Preface Acknowledgments xi xiii 1 Some Fundamentals of Infrared Spectroscopy Introduction The Energy of Electromagnetic Radiation Information That May Be Obtained from the Analysis of Infrared Spectra Comparison Techniques Fundamental Vibrations Stretching Vibrations Bending Vibrations Non-Fundamental Vibrations Predicting the Number of Fundamental Vibrations The Force Constant Some Theoretical Concepts Basic Sample Preparation Gaseous Samples Non-Volatile Liquids Volatile Liquids Solid Samples Other Sampling Techniques Some Suggestions and Comments on the Interpretation of Infrared Spectra 28 2 The Analysis of Infrared Spectra Hydrocarbons (Straight Chain) Hydrocarbons (Branched Chain) 37

9 viii Contents 2.3 Hydrocarbons (Cyclic) Alkenes Alkynes Ethers (Alkyl Alkyl) Ethers (Aryl Alkyl) Aliphatic Halides Amines Ketones and Aldehydes Alcohols Organic Acids Acid Halides Amides Esters Lactones Anhydrides Nitriles Aromatic Hydrocarbons Salts of Carboxylic Acid The Effects of Chelation on the Carbonyl Absorption Phosphines, Phosphites, Phosphonates and Phosphates Thioalcohols and Thiophenols Silanes Boranes Sulfones, Sulfates, Sulfonic Acids (and Their Salts), Sulfites and Sulfoxides Sulfones Sulfates Sulfonic Acids (and Their Salts) Sulfites Sulfoxides 88 3 Techniques, Innovations, and Applications in Infrared Spectroscopy Advances in Infrared Spectroscopy Fast Fourier Transform (FFT) The Michelson Interferometer 90

10 Contents ix 3.4 The FTIR Microscope and Microsampling Techniques Reflective Spectra Specular or External Reflectance Grazing Incidence Reflectance Reflective Absorption Spectra Diffuse-Reflectance Spectra Attenuated Total Reflectance (ATR) Theory of the ATR Cell Quantitative Infrared Analysis Combined Thermogravimetric Analysis and FTIR (TG/FTIR) The TG/FTIR Interface GC/MS, GC/FTIR and GC/MS/FTIR The GC/MS and GC/FTIR Interfaces Problems in Infrared Spectroscopy 113 Suggested Readings and References 161 Appendix 167 A.1 Infrared Group Frequencies (cm 1 ) 167 A.1.1 Infrared Solvents 167 A.1.2 Bands Related to Sample Preparation 167 A.2 General Infrared Assignments 168 A.3 Carbonyl Absorptions 168 A.3.1 Ketones (All Strong Absorptions) 168 A.3.2 α, β-unsaturated, Cyclic Ketones (cm 1 ) 168 A.3.3 Aldehydes (All Strong Absorptions) 169 A.3.4 Carboxylic Acids (All Strong Absorptions) (cm 1 ) 169 A.3.5 Amides 169 A Carbonyl Vibrations (Amide I Band, All Strong) (cm 1 ) 169 A N H Stretching Vibration (All Medium) 169 A.3.6 N H Deformation (Amide II Band, All Strong) 170 A.3.7 Esters Carbonyl (All Strong) 170

11 x Contents A.3.8 Anhydride Carbonyl (All Strong) 170 A.3.9 Hydrocarbon Chromophore 170 A.3.10 Substitution Patterns on Aromatic Ring (cm 1 ) 171 A.3.11 C C Multiple Bond Stretching (cm 1 ) 171 A.3.12 Acetylenic Types 172 A.3.13 Aromatic Skeletal-in-Plane Vibrations 172 A.4 Miscellaneous Compounds (Proximate Bands) 172 A.4.1 Alcohol and Phenols (Stretching) (cm 1 ) 172 A.4.2 Amines, N H Stretching 172 A.4.3 Unsaturated Nitrogen Compounds 173 A Nitriles, C N stretching 173 A C=N Stretching (cm 1 ) 173 A Nitro Compounds 173 A Nitroso Compounds 173 A Halogen Compounds C X Stretching 173 A Sulfur Compounds 173 A.5 Characteristic Overtone Patterns for Substitutions on Benzene 174 A.6 List of Infrared Symbols and Abbreviations 175 A.7 The Infrared Spectra of Some Common Chemicals Found in the Organic Chemistry Laboratory 176 Index 189

12 Preface This is an introductory text designed to acquaint undergraduate students with the basic theory and interpretative techniques of infrared spectroscopy. The author also believes that this material would be appropriate as an introductory text at the graduate level for those students lacking a background in the subject. Much of the material in this text has been used over a period of several years in teaching portions of a one-semester course in materials characterization and chemical analysis. In addition to infrared spectroscopy, the course also includes a discussion of mass spectrometry and nuclear magnetic resonance spectroscopy. For the most part, the students in the course have had at least one year of organic chemistry. Thus, they have had at least a cursory exposure to the theory and interpretation of organic spectra. In using this book in the course in materials characterization and chemical analysis, the author has devoted approximately 75 percent of the time to lecture discussions, with the remaining 25 percent devoted to the hands-on use of the various instruments at our disposal. However, depending on the needs and assessment of the instructor, the text could serve solely as a lecture text for a one-semester course in infrared spectroscopy or it could be used to teach the infrared portion of a broader course in materials characterization and chemical analysis. In this undertaking, the author has tried to put together a book that is readable at the undergraduate or beginning graduate level. To do this, the text has been interspersed with many illustrations, examples, problems, and an extensive bibliography. In developing an introductory text, out of necessity, many more advanced spectroscopic concepts have been excluded. Despite these exclusions, the text should serve to give the student a solid

13 xii Preface background in the area discussed. It is hoped that those using the text would be sufficiently inspired to continue with more advanced study in the area of infrared spectroscopy. Students learn best by examples. Accordingly, the book includes many examples of the spectra representing a broad range of organic compounds. Thus, the text has been made more readable. No author is entirely satisfied with his or her final works. Even as the final draft of the text is reviewed, there is an inclination to go back and expand, rephrase, and modify certain sections. Since this effort could continue for some time, what has been done is reluctantly submitted with the recognition that there are many areas for improvement. In a desire to improve upon this material, reliance is placed upon you, the students and the professors. Your recommendations and notification of the errors of submission and omission will be appreciated. James M. Thompson

14 Acknowledgments Several organizations and companies have been very generous in allowing the use of their infrared spectra in this text. This generosity has eased the writing of this text, and the author expresses his sincere appreciation to all involved.

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